ABSTRACT Brain vascular malformations and blood-brain barrier defects represent important substrates for developing stroke, epilepsy and other neuropathological diseases. The most common type of brain malformation closely associated with stroke are the cerebral cavernous malformations (CCMs), which affect approximately 0.5% of population. Recognized as familial or sporadic, CCMs are characterized as a single or multi-cluster of enlarged capillary-like channels with a single layer of endothelium and without intervening brain parenchyma. There are specific alterations in the brain endothelial barrier components that ultimately lead to vascular hyperpermeability, extravasation of red cells and an inflammatory response in brain parenchyma. Although significant progress has been made in defining the genes mutations involved in the inherited CCM3 form, the intra- and intercellular pathogenic mechanisms responsible for vascular hyperpermeability are still largely unknown. The proposed study is designed to elucidate critical molecular events in the maintaining the integrity and impairment of the brain endothelial barrier in CCM3. It will highlight the link between signaling molecules CCM3 and connexin 43 isoform (Cx43CT-20kDa), one of the protein identify by our screening analysis to be highly expressed in condition of loss of CCM3 function in brain endothelial cells. Specifically, it will be evaluated a) the functional and morphological consequence of Cx43CT-20kDa on brain endothelial barrier stability with loss of CCM3 and b) signaling pathways triggered by CCM3 absence involved in regulating synthesis of Cx43CT-20kDa. Collectively, these studies will provide new information related to the mechanisms of maintenance of brain endothelial barrier that is relevant also to multiple disease states and will, hopefully, elucidate novel therapeutic strategies to restore the vascular hyperpermeability.